A fuel supply system of the fuel injection type in an internal combustion engine for automobiles is generally the like shown in FIG. 3, wherein fuel 2 in a fuel tank 1 is sent out of the fuel tank 1 by a low-pressure pump 3, filtered through a filter 4 and, following receiving pressure adjustment by a low-pressure regulator 5, supplied to a high-pressure fuel supply apparatus 6, or a high-pressure pump. Fuel is rendered high pressure by the fuel supply apparatus 6 only in the quantity necessary for fuel injection and supplied into common rails 9 of an internal combustion engine (not shown). The remainder of the fuel is released through an electromagnetic valve 17 into the space between a low-pressure damper 12 and a suction valve 13. The quantity necessary for fuel injection is determined by a regulation unit (not shown), which also regulates the electromagnetic valve 17. The high-pressure fuel thus supplied is injected in high-pressure spray into a cylinder (not shown) of an internal combustion engine from a fuel injection valve 10 connected to the common rails 9. A filter 7 and a high-pressure relief valve 8 open in the event of unusual pressures within the common rails 9 (the high-pressure relief valve opening pressures) to prevent the failure of the common rails 9 and the fuel injection valve 10.
The high-pressure fuel supply apparatus 6, or a high-pressure pump, comprises a filter 11 for filtering the supplied fuel, the low-pressure damper 12 for absorbing the pulses of low-pressure fuel, and a pump 16 that applies pressure to the fuel supplied through the suction valve 13 and discharges the high-pressure fuel through a discharge valve 14 and a fuel pressure holding valve 15. As shown in FIG. 4, a fuel pressuring room 24 constituted by a plunger 26, a sleeve 25 and a plate 102 of the pump 16 plus the suction valve 13 and the discharge valve 14 is linked to the space between the low-pressure damper 12 and the suction valve 13 via the electromagnetic valve 17.
FIG. 4 shows the details of a structure of a conventional high-pressure fuel supply apparatus like the high-pressure fuel supply apparatus 6. In FIG. 4, the high-pressure fuel supply apparatus 6 is provided with a cylindrical sleeve, or a cylinder 25 that forms inside thereof the pressuring room 24 being accommodated within a casing 21 and having a suction port 22 and a discharge port 23 for fuel. Within the cylinder 25, the plunger 26 that is supported slid ably in the line of the axis for making the volume the pressuring room 24 variable within the cylinder 25 is disposed, and a compression spring 27 is disposed at the inner end (the upper end in the Figure) of the plunger 26, and at the outer end (the lower end in the Figure) thereof a working member, or a tappet 28, that receives a driving force from outside through an unillustrated engine camshaft and transmits the driving force to the plunger is fitted and fastened. Thus, the plunger 26 and the tappet 28 constitute a piston 29 of the high-pressure fuel supply apparatus 6.
In FIG. 4, the high-pressure fuel supply apparatus 6 comprises integrally the pump 16, or a plunger pump, the electromagnetic valve 17 connected to the pressuring room 24 and the low-pressure damper 12.
The high-pressure fuel supply apparatus 6 also comprises a casing 30 for preventing the fuel leaking out of the space between the cylinder 25 and the piston 29 from leaking outside by surrounding substantially the cylinder 25 and the piston 29, and a sealing means 31 made of rubber for sealing the space between the casing 30 and the plunger 26 of the piston 29.
A high-pressure fuel supply apparatus like the high-pressure fuel supply apparatus 6, in which the plunger piston 29 is driven up and down in FIG. 4 by the driving cam disposed coaxially with the unillustrated engine camshaft sucks up and discharges fuel. During the process, through the opening of the electromagnetic valve 17 at the time when a certain quantity of fuel has been discharged into the common rails 9, the high-pressure fuel in the pressuring room 24 is released to the suction side at a lower pressure, and then no fuel is pumped into the common rails 9. Through the control of the timing of opening of the electromagnetic valve 17, the discharge from the fuel supply apparatus 6 is variably adjusted and controlled.
In the conventional high-pressure fuel supply apparatus thus constructed 6, the piston 29 for applying pressure to fuel is used as the member on the shaft side, and as the member on the opposing side a sealing member 31 made of rubber is disposed in the sealing means 31 for preventing fuel in the high-pressure fuel supply apparatus 6 from leaking into the engine room. For the prevention of abrasion of the seal 31, an oil film is formed in the sealing section at the part where the plunger 26 that leads fuel or engine oil during the reciprocation of the piston 29 comes into contact with the lips of the rubber sealing means 31 so that the seal 31 does not wear away.
Because the structure like this is a structure allowing and utilizing a certain level of minor leakage rather than providing a perfect sealing, there are such problems as a significant variance of the lubrication condition in the sealing section, occurrence of abrasion of the sealing section and an increase in the quantity of leakage, depending on the condition of the surface of the sealing section on the shaft side, the speed of movement of the shaft, the shape and interference of the rubber lips and the state of fuel and engine oil around the lips.
Further, in the high-pressure fuel supply apparatus 6, the piston 29 applying pressure to fuel is the most important part, and so a great deal of time is needed in evaluation. As to durability in particular, abrasion with and seizure to the sleeve 25 that constitutes the fuel pressuring room 24 together with the piston 29 and is engaged with the piston 29 with a certain level of space in-between pose a problem. In the event of occurrence of such a problem in the sealing section in a conventional apparatus like this, it is necessary to evaluate concurrently the effect of the piston 29 on the abrasion with and seizure to the sleeve 25, and a great deal of time is needed in evaluation. In addition, because of the generation of a limitation in the measures for the side of the piston 29, a further time is needed in evaluation.
The present invention therefore has as its object the provision of a high-pressure fuel supply apparatus, in which the durability of the fuel sealing section is improved and additionally the evaluation time is reduced.